Where to set duty cycle for a successful Ca emissions test?

[Tinker]

Hi all,

I have get the wife`s 87 190e 16V smog tested at a test only center. Anyone tell me where you set your duty cycle. Probably close to the factory specs (50%?), but should I lean it slightly?
Currently its adjusted at 50% duty cycle and approximately -2.3 ma at the EHA. Go leaner? Or leave it and try. $45 a pop.

Thanks.

Tinker

[stevebfl]

It shouldn't matter. The point of this control system is to make the cars mixture be an exact amount. It compensates up to its capabilities for any change you make. The only exception to this is that all mixture in non steady state is made from base mixture at the correction of the moment.

The point is was your car in CLOSED LOOP. You state 50% and -2.3ma. These numbers beter be moving. A fixed 50% duty cycle indicates an open O2 sensor circuit (or no response - such as when cold). The EHA current should be at 0 when the duty cycle is at 50%. I'm hoping that the 50% was the high point of a 5% swing as this would go with a momentary -2.3 ma fuel correction
The EHA current should be also swinging up and down a few ma.

It is this correction lean to rich to lean to rich that is CLOSED LOOP control. If it is happening you shouldn't fluck the test. Making sure the cat is hot is the rest of the story.

[Tinker]

Steve,

Thanks for the quick response. Yes the readings are fluctuating and the numbers posted are averages from the Fluke meter.

The -2.3ma EHA doe concerns me. Is it better to adjust the EHA to an average 0 ma or set the duty cycle close to 50% and let the EHA do its thing? Per your article, the -2.3ms would indicate a rich mixture. Is something wrong/off to have this combination?

As always, THANK YOU.

Tinker

[stevebfl]

Training says that 50% is the proper spot. Training will also say that it doesn't matter as I have pointed out.

BUT, -2.3 is the way I set them up. They still have plenty of run for correction although it is no longer 50/50. I prefer basic fuel correction a little richer for some performance reasons. Remember electronically everything is made to be the same mixture, but it doesn't happen instantly. It takes a half second or more. For instantaneous throttle response I like the basic mix slighly richer. If you run around jumping on and off the gas the thing might not stay in emissions control.

It also is a little richer cold, as electronic control is only woking in fixed mode (no lambda correction til O2 sensor is hot).

It is also a very small amount.